A method controlling surface defects in metal-coated strip

摘要

A method of controlling "rough coating" and "pinhole-uncoated" surface defects on a steel strip coated with a aluminum-zinc-silicon alloy. The alloy has 50-60 % wt Al, 37-46 % wt Zn and 1.2-2.3 % wt Si. The method includes heat treating the steel strip in a heat treatment furnace and thereafter hot-dip coating the strip in a molten bath and thereby forming a coating of the alloy on the steel strip. The method is characterized by controlling the concentration of (i) strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2 ppm.